Hi David,
Here is my first crack at the cover image for "Rocket's Red Glare." I have worked off of the original idea you suggested (the image of a city growing on the face of a quarter,) and stuck to a pretty literal interpretation of the material.
I began with a drawing of a quarter as seen from a low angle.

Next, I created a generic city texture, trying to match the angle of the first sketch, and leaving all the detail for a later stage.

And, finally, a composite of the two images in photoshop.

Here is a slightly lighter rendering, letting the line work tell more of the story.

This is, of course, just a sketch. I will be doing a lot of tinkering with the layout of the city, adding detail and adjusting the scale of buildings relative to the quarter.
The challenge in rendering the final piece will be to make both the city, and the quarter details visible, without loosing the quick read of the image in visual clutter.
Please let me know if you have any suggestions as I go into a second series of sketches. I am looking forward to adding some recognizable building types (banks and churches) as well as surface detail such as water towers, billboards, maybe even some cars and trees. I should have something new for you to look at by this time next week.